The invention relates to the field of dielectric structures also known as photonic crystals, and in particular to structures with high reflectivity characteristics that are made of biocompatible materials. Biocompatibility is defined as any material that can come in contact with at least one part of the body without causing significant health hazards. For example, an edible material is a subset of the biocompatible materials since it could come in contact with the digestive system without causing significant health hazards. Further examples include metabolizable materials, injectable materials or material which are introduced to the body via bodily systems, e.g., respiratory, epidermal, etc.
Dielectric structures can have a variation in the index of refraction in one, two or three directions. Depending on the details of the structure, one can form photonic band gaps in one or more directions. Devices that have photonic band gaps are used in a wide variety of optical devices that typically utilize the frequency selective reflectivity that these structures exhibit. The simplest system being a multilayer film, including for example various three dimensional arrangements of spheres and other arrangements of dielectric media. A comprehensive theory on the optical properties of these dielectric structures has been published (see Joannopoulos et al., Photonic Crystals Molding the Flow of Light, Princeton University Press, 1995).
The materials system or dielectric structure, for example photonic crystal, of the invention includes a plurality of materials that are biocompatible. The materials have different indices of refraction for the wavelength of operation and are assembled into a dielectric structure having a photonic band gap in one or more directions. The assembly process yields a structure with a particular spatial arrangement of materials with different indices of refraction which is completely biocompatible and has the property of reflecting light at a particular predetermined range of frequencies, as well as other properties associated with photonic band gaps. These structures can exhibit photonic band gaps that can be engineered to be broad or narrow and be centered on different parts of the spectrum UV, visible IR or longer wavelengths. The materials used can have microwave transparency or be made to reflect microwaves. Possible applications include edible reflectors for visible to impart a particular color to the food or specular appearance, heat shields to minimize radiative and evaporative and convective heat losses, and as a UV protection layer.